Stripping layered material by wet jet milling technique

Abstract

Stripping of layered materials by wet jet milling techniques is disclosed. A system for peeling a layered material includes, in combination: a peeling station operating on a dispersion of a volume of a layered precursor material, including a wet jet milling device; downstream of the stripping station, a collection station operating on a dispersion of a volume of at least partially stripped material, the stripping station and the collection station being connected to each other by a fluid communication path along which there is inserted a flow regulation device adapted to assume a first operating configuration in which the communication path between the stripping station and the collection station is interrupted, the stripping station is adapted to perform a predetermined number of wet jet milling cycles on a volume of a dispersion of layered precursor material; and a second operational configuration in which the communication path between the stripping station and the collection station is continuous, the stripping station being adapted to deliver a volume of a previously ground dispersion comprising at least partially stripped material to the collection station and being arranged in communication with the supply chamber to supply a further volume of a dispersion of layered precursor material that must be stripped.

Description

[0001] This application is a divisional application of the invention patent application filed on November 24, 2016, with application number 201680069073.3 and invention title "Removing Layered Materials by Wet Jet Grinding Technology". Technical Field

[0002] This invention relates to a method for peeling off layered materials, and more particularly to a method for peeling off layered materials by means of hydrodynamics, especially by liquid jet micronization technology, more commonly known as wet-jet abrasive technology.

[0003] Specifically, the present invention relates to a system for peeling off layered materials and a method for peeling off layered materials. Background Technology

[0004] The exfoliation of materials with layered crystal habits (such as, for example, graphite, boron nitride, tungsten disulfide (IV), tungsten diselenide (IV), molybdenum disulfide, bismuth telluride, and black phosphorus) is a difficult process in both basic and applied research contexts and in industrial production contexts related to the technology of two-dimensional material fabrication.

[0005] Mechanical peeling of layered materials is a widely used technique for obtaining high-quality two-dimensional sheets. However, mechanical peeling is not suitable for mass production and therefore not applicable to industrial applications.

[0006] In industrial applications requiring high production volumes, known liquid phase stripping technology can meet the quality and quantity requirements of the produced materials.

[0007] The most widely used method for liquid-phase exfoliation is ultrasonic treatment, which involves exposing a layered crystalline material to sound waves, particularly ultrasound, propagating in a collection container in which the layered material is dispersed in a liquid phase (often called a solvent). The choice of liquid phase depends on the properties of the layered material itself, particularly that the surface tension of the liquid phase must be comparable to the surface energy of the dispersed layered material. Ultrasound produces a cavitation effect, in which bubbles are formed within the block of layered material (and any sheets that may be obtained from it), and when they implode, they generate microjets of liquid and shock waves that suddenly act on the surface of the material. These shock waves induce compressive stress along a plane perpendicular to the material layers, and this compressive stress at the interface induces tensile stress that leads to the desired detachment of the material sheets.

[0008] Liquid-phase exfoliation via ultrasonic treatment produces a heterogeneous mixture of single-layer, double-layer, or multi-layer sheets and a large amount of unexfoliated layered material. Disadvantages include the fact that ultrasonic treatment is a violent process, generating localized high temperatures (approximately several thousand K), extreme pressures (several thousand atmospheres), and rapidly fluctuating localized heating / cooling gradients. These factors contribute to material degradation, particularly the cracking of the produced sheets. Therefore, this technology is unsuitable for producing sheets with large surface dimensions, such as hundreds of micrometers.

[0009] Experiments have shown that the quality yield between the starting material and the final product is well below 10% during the ultrasonic peeling process. Furthermore, the ultrasonic treatment process is extremely time-consuming, ranging from minutes to hundreds of hours, and requires continuous temperature control because the treated material is exposed to high localized heating.

[0010] Another drawback of ultrasonic treatment is its unsuitability, as it produces thin sheets of material that are easily oxidized, and therefore requires a controlled atmosphere for production / processing.

[0011] To overcome the technical drawbacks of ultrasonic processing, fluid dynamics-based liquid phase exfoliation techniques have recently been studied, particularly for the exfoliation of large-volume graphite.

[0012] In hydrodynamic exfoliation, the volume of a layered precursor material is freely immersed in a dispersed liquid phase, typically called a solvent, and repeatedly exfoliated at different locations and orientations by the hydrodynamic forces applied by the flow of the liquid phase. These techniques are fundamentally different from ultrasonic processing techniques and could be effectively used for the industrial-scale production of two-dimensional sheets of layered materials, particularly for the production of graphene sheets from graphite.

[0013] Typically, known hydrodynamic milling techniques cannot effectively exfoliate layered materials, and while suitable for manufacturing them on an industrial scale, they cannot be considered effective alternatives to ultrasonic processing (i.e., sheets with a single or a few layers of atoms) for producing high-quality nanoscale two-dimensional flakes. These techniques cannot be used to obtain materials required for specific technical applications, such as graphene flakes used in ink formulation.

[0014] In hydrodynamic exfoliation technology, wet jet milling or liquid jet micronization is widely used for the colloidal homogenization of bulk (nano) materials or their reduction into powder, and has been successfully used in industrial grinding or dispersion processes.

[0015] Examples of high-pressure liquid jet milling equipment include commercially available instruments known by the names “Nanomaker” (manufactured by Advanced Nanotechnology Co., Ltd.), “Nanomizer” (manufactured by Nanoizer Inc.), “Nanomizer” (manufactured by Yoshida Kikai Co. Ltd.), and “Nano Jet Pal” (manufactured by Jokoh Co. Ltd.).

[0016] The article “A fluid dynamic route for the production of graphene and its analogues” by Min Yi, Zhigang Shen, and Jinyang Zhu, published in Chinese Science Bulletin 59(16), pp. 1794-1796 in 2014, is relevant to this article. A fluid dynamics route for producing graphene and its analogues The document describes a fluid dynamics technique for the large-scale production of graphene and similar two-dimensional materials, in which the volume of layered materials such as graphite, boron nitride, molybdenum disulfide, and tungsten disulfide is stripped into a single monolayer or remains two-dimensional but comprises a structure of several atomic layers.

[0017] Many fluid dynamic phenomena contribute to delamination, including cavitation, which generates forces perpendicular to the plane of the layered material; shear forces caused by the viscosity of the dispersed phase, which induce forces coplanar with the plane of the layered material; and turbulence caused by the interaction of fluid jets, which induces lateral forces acting parallel to the plane of the layered material.

[0018] Graphite stripping via wet jet milling is performed in an open loop and has not been optimized to reduce defects in the wafers and increase the relatively low yield by about 10%. Summary of the Invention

[0019] The purpose of this invention is to overcome the shortcomings of known technologies and to provide a method for peeling layered materials that enables the production of sheets with a minimum thickness down to the limit of a single atom, and large lateral dimensions (about micrometers) and / or surface dimensions (tens of square micrometers).

[0020] Specifically, one object of the present invention is to optimize wet jet milling technology by controlling the hydrodynamic phenomena responsible for stripping the material, particularly by reducing turbulence in the liquid phase, which in the known art causes an undesirable cavitation process that helps reduce the lateral dimensions of the two-dimensional sheets produced.

[0021] Another object of the present invention is to provide an apparatus for implementing an optimized hydrodynamic stripping process, which is adapted to enable the large-scale production of two-dimensional sheets of material to meet industrial requirements, while controlling the lateral and / or surface dimensions of the sheets.

[0022] These objectives are achieved by the stripping system of the present invention.

[0023] Another subject of the present invention is the claimed peeling method.

[0024] The content of the specific implementation should be understood as constituting an integral part of this specification.

[0025] In summary, this invention is based on the principle of exfoliating layered materials to manufacture two-dimensional materials such as graphene, boron nitride, phosphorene (a single atom layer of black phosphorus), transition metal di- and trisulfides (among which, for example, tungsten disulfide (IV), tungsten diselenide (IV), molybdenum disulfide, and bismuth telluride). Through hydrodynamic means, liquid jet micronization technology (wet jet milling) is applied to a mixture of layered materials in a predetermined dispersed phase, and the physicochemical parameters of the dispersed phase and the hydrodynamic parameters of the mixture are controlled to achieve controlled exfoliation and the desired lateral dimensions of the two-dimensional sheets.

[0026] In contrast to other exfoliation techniques, liquid jet micronization has proven suitable for the continuous cyclic production of two-dimensional sheets from layered materials and can be applied to the exfoliation of large quantities of material sheets, thus representing a very useful technique for extending the processing of these materials at the industrial level.

[0027] During the exfoliation process, it is crucial to efficiently transfer energy from the liquid medium to the processed layered material in order to exfoliate it, while minimizing cracks in the basal surface. The use of liquid jet micronization technology (wet jet milling) to generate the necessary exfoliation force enables the exfoliation of nanoscale two-dimensional flakes from a given volume of precursor material (approximately several hundred micrometers in size), dispersing them in a dispersed phase without compromising their physicochemical and (opto)electronic properties.

[0028] The exfoliation method according to the invention includes a first step of preparing a mixture (dispersion) of precursor layered materials having a suitable dispersant fluid phase, and a subsequent step of exfoliating the material by exposing it to one or more wet jet milling cycles in a milling apparatus capable of generating hydrodynamics in the mixture by compressing the dispersant fluid phase. Finally, the exfoliated material undergoes a purification step including possible centrifugation and, for example, separation from the dispersion phase by sedimentation, a process that allows for the selection of flakes based on their lateral dimensions.

[0029] First, the number of grinding cycles is determined based on the properties and quantity of the layered material that must be processed, i.e. its concentration in the dispersed phase, and based on the dispersed phase itself, i.e. the number of times the mixture of precursor materials in the dispersed phase passes through the grinding device.

[0030] Advantageously, the method according to the invention can be fully automated in a continuous cyclic processing / production line, comprising an exfoliation station (exfoliation site, exfoliation location) and a collecting station (collecting site, collection location) downstream of the exfoliation station, operating in parallel on dispersions of different volumes (dispersions of precursor material and (at least partially) dispersions of exfoliating material, respectively). In a processing configuration where the communication path between the stations is closed, the exfoliation station causes the respective dispersions of precursor material to undergo wet jet milling in a continuous cycle, and the collecting station, in parallel, causes the respective (at least partially) dispersions of exfoliating material to undergo possible centrifugation and conveniently separate from the dispersed phase by sedimentation. In a material supply / discharge configuration where the communication path between the stations is open, the exfoliation station supplies new precursor material from a supply container and conveys pre-milled volumes of dispersions in parallel to the collecting station.

[0031] Even more advantageously, the methods and apparatus according to the invention have proven suitable for processing materials that require a controlled atmosphere, where exposure to the open air would likely impair their physicochemical properties.

[0032] The dispersed phase (density, viscosity) and concentration, as well as the structure of the grinding apparatus and the selection of its compression parameters for generating the hydrodynamic forces responsible for peeling, enable controlled peeling of the layered material without breaking it, because the peeling force is sufficient to break the weak van der Waals electrostatic bonds established between the precursor material layers, but not enough to break the covalent bonds established within each layer.

[0033] The choice of the dispersed phase for the stripping and dispersion process is determined by the physicochemical properties of the layered material to be stripped. In particular, the surface tension or Hansen solubility parameter of the dispersed phase must be close to the corresponding parameter specific to the material being stripped. Attached Figure Description

[0034] Other features and advantages of the invention will be set forth in more detail in the following detailed description of embodiments provided by way of non-limiting examples with reference to the accompanying drawings, wherein: Figure 1 This is a schematic illustration of a grinding apparatus for carrying out the method according to the invention; Figure 2A and Figure 2B This is a schematic illustration of a stripping device suitable for use in a continuous cycle production line, showing two different steps in the method. Figure 3 Electron microscope images of the stripped sections obtained by the method according to the invention are shown; and Figure 4This is a graph showing a comparison between the Raman spectra of graphite, graphene ink obtained using an ultrasonic processing process, and graphene ink obtained by the method according to the present invention. Detailed Implementation

[0035] Figure 1 A wet jet milling apparatus 10 is schematically shown, comprising a supply chamber 12 adapted to contain a mixture of layered materials in a predetermined dispersed phase; a compression device 14 connected to the supply chamber 12 via a feed pipe 16; and a milling device 18 located downstream of the compression device and connected to the supply chamber 12 via an outlet pipe 20 to form a recirculation path. The compression device is arranged to compress a predetermined volume of mixture drawn from the supply chamber into a pipe having a first compression section toward the milling device. A heat exchanger 22 may advantageously be present on the pipe 20 to control the temperature of the dispersion from downstream of the milling device itself.

[0036] The grinding apparatus includes multiple fluid paths adapted to guide a mixture injected at high pressure by a compression device into a pipe with a smaller cross-section relative to a first compression section, thereby generating one or more linear jets conveyed toward at least one collision section, wherein the movement of the layered material in the fluid and the collisions between the fluid jets cause the material to peel off.

[0037] Figure 2A and Figure 2B Details of the peeling device according to the invention are shown, including references Figure 1 The wet jet milling apparatus of the type shown and discussed, wherein the above-mentioned Figure 1 The same or functionally equivalent elements or components shown are indicated using the same reference numerals used in the description of the figure.

[0038] and Figure 1 Unlike the simplified diagram, the wet jet milling apparatus is integrated into a continuous circulation stripping device that includes a separation chamber 30 downstream of the milling apparatus to separate the treated material from the dispersed phase and a collection chamber 40 for the treated material.

[0039] The feed pipe 16 and the outlet pipe 20 of the grinding device have a common flow regulating device, such as a four-way distribution valve 50 suitable for one of two predetermined configurations, namely a first open-circuit configuration and a second closed-circuit configuration.

[0040] In the first open-circuit configuration used during the material supply / discharge step, the feed pipe 16 from the supply chamber 12 is connected to the compression unit 14 of the grinding apparatus via a distribution valve 50. Simultaneously, the outlet pipe 20 from the grinding apparatus 18 is connected to a separation unit 30 via the distribution valve 50. In a preferred embodiment, the separation unit 30 is a purification and sedimentation device, such as a centrifuge, to separate the material stripped in this manner from the dispersed phase.

[0041] Activation of the compression device 14 allows the dispersion containing the treated material to be pumped from the grinding device to the separation device 30 at the end of the cycle and simultaneously supplied to the grinding device with a dispersion containing additional material to be treated by extracting it from the supply chamber 12 in a further cycle.

[0042] In the second closed-loop configuration used during the material processing step, the outlet pipe 20 from the grinding device 18 is connected to the compression device 14 via the distribution valve 50 in a recirculation configuration (in which the path to the separation device 30 is interrupted to allow a predetermined number of consecutive stripping cycles to be performed on the same volume of dispersion).

[0043] After the material has been processed, that is, when the material has reached the satisfactory predetermined stripping conditions, or when the predetermined number of cycles has been performed, the dispensing valve 50 is switched back to the first open-circuit configuration used in the material supply / discharge step, and the sequence of the above steps is repeated.

[0044] Preferably, a check valve 55 is also shown in the drawings along the path from the supply chamber 12 to the compression device 14 and from the grinding device 18 to the separation device 30.

[0045] Of course, as those skilled in the art will understand, embodiments also included within the scope of this invention may include valve systems other than the four-way distribution valve described above, such as a combination of several T-valve components controlled synchronously in a suitable manner.

[0046] When implementing the method according to the invention, a mixture or dispersion of layered materials in a predetermined dispersed phase is prepared according to a predetermined concentration ratio, preferably 1 to 5% by weight.

[0047] More specifically, the material that needs to be stripped typically has 10 to 5000 m, preferably 100 m to 5000 One or more volumes of layered material blocks on the side of m are placed in a dispersion (or suitable colloidal suspension), wherein the dispersed phase is predetermined based on the physicochemical properties of the layered material. The dispersed phase can be selected from a variety of liquid phases to suitably tune the rheological properties of the two-dimensional material to be produced.

[0048] The dispersed phase (or mixture of dispersed phases) is chosen such that its surface tension is close to the surface energy of the layered material to be peeled (for defects, the surface tension of the dispersed phase (or mixture of dispersed phases) is close to the surface energy of the layered material to be peeled), preferably less than 30 mN / m (or 30 mJ / m) of the material's surface energy. 2 Stable dispersion requires the Gibbs free energy (ΔG) of the mixture. mix () can be negative or zero: ΔG mix =ΔH mix -TΔS mix , Where ΔH mix It is the enthalpy of the mixture, T is the temperature, and ΔS mix It refers to the change in entropy during the mixing process.

[0049] For example, for a graphene / N-methyl-2-pyrrolidone mixture, the entropy change ΔS per unit surface area mix It has an order of approximately 0.1 mJ / m. -2 K -1 Therefore, the dispersion and stabilization of graphene sheets in the dispersed phase or mixture of dispersed phases also require a smaller ΔH value. mix value.

[0050] In addition, the surface energies of graphene and the dispersed phase must be very close. The surface tension γ of the dispersed phase is converted into the surface entropy S of the dispersed phase. Sur Surface energy E of the material Sur The relationship is as follows: γ = (E Sur -T S Sur ) Where S Sur The value is typically between 0.07 and 0.14 mJ / m. -2 K -1 0.1 mJ m -2 K -1 The general value is universally accepted and used.

[0051] Considering the example of graphene again, the estimated surface energy reported in the literature is between 70 and 80 mJ / m². -2 Within this range, therefore at ambient temperature, the surface entropy S of the dispersed phase described above is... Sur The ideal dispersion value is 40 to 50 mN m -1The surface tension value γ. The dispersed phase or dispersed phase mixture used to carry out the present invention must meet this value. A dispersed phase or dispersed phase mixture having a surface tension of + / -20% of this range, or even more preferably + / -10% of this range, can be effectively used to exfoliate graphite into graphene.

[0052] Regarding E Sur and S Sur The appropriate value, the same considerations apply to all layered materials that must be stripped by hydrodynamic methods in the dispersed phase or mixture of dispersed phases.

[0053] Alternatively, the dispersed phase or a mixture of dispersed phases can be selected based on the Hansen solubility parameter (HSP).

[0054] Hansen's solubility parameter subdivides the total cohesive energy of a liquid into three independent interaction parameters, which describe (a) the intermolecular forces between molecules (dipoles) p (a) Energy derived from intermolecular dispersion forces, and (b) Energy derived from intermolecular dispersion forces. D (c) Energy generated by hydrogen bonds or electron exchange parameters between molecules H ).

[0055] Therefore, the choice of dispersed phase or dispersion mixture depends on the match between the dispersed phase and the Hansen solubility parameter of the material to be exfoliated. Specifically, the ideal dispersed phase or dispersion mixture for dispersing the material is one with a Hansen solubility parameter (for the Hansen coordinates of the dispersed phase) within the Hansen space that best approximates the Hansen coordinates of the material. Thus, the smaller the Hansen distance between the Hansen coordinates of the dispersed phase or dispersion mixture and the Hansen coordinates of the material, the greater the interaction between the dispersed phase and the layered material.

[0056] This relationship can be expressed by the following equation: r 2 =( D溶剂 - D材料 ) 2 +( P溶剂 - P材料 ) 2 + +( H溶剂 - H材料 ) 2

[0057] In order to obtain the optimal interaction between the dispersed phase and the material, r It should be between 0 and 20 MPa 1 / 2 Within the range, preferably from 0 to 10 MPa 1 / 2 Within the range, preferably between 0 and 5 MPa 1 / 2 Within the range.

[0058] For example, the surface tension of the dispersed phase used to exfoliate graphite into graphene is between 22.5 and 67.5 mN / m, preferably between 27 and 63 mN / m, even more preferably between 36 and 54 mN / m, advantageously between 40.5 and 49.5 mN / m, more specifically about 45 mN / m, or, in a completely equivalent manner, the Hansen solubility parameter of the dispersed phase. p , D , H 9 to 27 MPa respectively 1 / 2 5 to 15 MPa 1 / 2 3.5 to 10.5 MPa 1 / 2 Preferably, the pressure is between 12.6 and 23.4 MPa. 1 / 2 7 to 13 MPa 1 / 2 4.9 to 9.1 MPa 1 / 2 Even more preferably, they are 14.4 to 21.6 MPa. 1 / 2 8 to 12 MPa 1 / 2 5.6 to 8.4 MPa 1 / 2 Advantageously, the values ​​ranged from 16.2 to 19.8 MPa. 1 / 2 9 to 11 MPa 1 / 2 6.3 to 7.7 MPa 1 / 2 More specifically, approximately p = 18 MPa 1 / 2 , D = 10 MPa 1 / 2 and H = 7 MPa 1 / 2 .

[0059] The procedure is similar for other materials.

[0060] For example, in the case of molybdenum disulfide (MoS2), the surface tension of the dispersed phase used to exfoliate the three-dimensional crystal into sheets must be between 12.5 and 67.5 mN / m, preferably between 15 and 63 mN / m, even more preferably between 20 and 54 mN / m, advantageously between 22.5 and 49.5 mN / m, even more advantageously between 25 and 45 mN / m, or the Hansen solubility parameter of the dispersed phase. p , D , H The values ​​ranged from 8.5 to 28.5 MPa. 1 / 2 3 to 18 MPa 1 / 2 2.2 to 12.7 MPa 1 / 2 Preferably, the values ​​are 11.9 to 24.7 MPa. 1 / 2 4.2 to 15.6 MPa 1 / 2 3.1 to 11 MPa 1 / 2 Even more preferably, they are 13.6 to 22.8 MPa. 1 / 2 4.8 to 14.4 MPa 1 / 2 3.6 to 10.2 MPa 1 / 2 Advantageously, the values ​​ranged from 15.3 to 20.9 MPa. 1 / 2 5.4 to 13.2 MPa 1 / 2 4 to 9.3 MPa 1 / 2 Even more advantageously in the following range p = 17-19 MPa 1 / 2 , D =6-12 MPa 1 / 2 and H = 4.5-8.5 MPa 1 / 2 Inside.

[0061] In the case of tungsten disulfide (WS2), the surface tension of the dispersed phase used to exfoliate the three-dimensional crystals into flakes must be between 20 and 67.5 mN / m, preferably between 28 and 58.5 mN / m, even more preferably between 32 and 54 mN / m, advantageously between 36 and 49.5 mN / m, and even more advantageously between 40 and 45 mN / m, or the Hansen solubility parameter of the dispersed phase. p , D , H8 to 27 MPa respectively 1 / 2 2.5 to 21 MPa 1 / 2 1 to 28.5 MPa 1 / 2 Preferably, the pressure is between 12.8 and 21.6 MPa. 1 / 2 4 to 16.8 MPa 1 / 2 1.6 to 22.8 MPa 1 / 2 Even more preferably, they are 14.4 to 19.8 MPa. 1 / 2 4.5 to 15.4 MPa 1 / 2 1.8 to 20.9 MPa 1 / 2 And advantageously within the following scope p = 16-18 MPa 1 / 2 , D =5-4 MPa 1 / 2 and H = 2-19 MPa 1 / 2 Inside.

[0062] In the case of hexagonal boron nitride (BN), the surface tension of the dispersed phase used to exfoliate the three-dimensional crystal into sheets must be between 15 and 60 mN / m, preferably between 21 and 52 mN / m, even more preferably between 24 and 48 mN / m, advantageously between 27 and 44 mN / m, and even more advantageously between 30 and 40 mN / m, or the Hansen solubility parameter of the dispersed phase. p , D , H The values ​​ranged from 8.5 to 28.5 MPa. 1 / 2 2 to 15 MPa 1 / 2 2 to 15 MPa 1 / 2 Preferably, the values ​​are 11.9 to 24.7 MPa. 1 / 2 2.8 to 13 MPa 1 / 2 2.8 to 13 MPa 1 / 2 Even more preferably, they are 13.6 to 22.8 MPa. 1 / 2 3.2 to 12 MPa 1 / 2 3.2 to 12 MPa 1 / 2 Advantageously, the values ​​ranged from 15.3 to 20.9 MPa. 1 / 2 3.6 to 11 MPa 1 / 2 3.6 to 11 MPa 1 / 2 Even more advantageously in the following range p = 17-19 MPa 1 / 2 , D = 4-10 MPa 1 / 2 and H = 4-10 MPa 1 / 2 Inside.

[0063] The peeling process is carried out by wet jet milling. The operating parameters of the compression device for the milling apparatus are set and the number of compression paths is programmed to ensure that all the layered materials are milled a sufficient number of times to achieve the desired (all or almost all) peeling.

[0064] Controlling the pressure applied to the dispersion by the compression device is important to avoid or at least limit excessive acceleration of the dispersion in the pipes of the grinding device. Such acceleration can induce turbulence in the impact section, which can lead to undesirable cavitation effects.

[0065] Finally, in order to obtain high-quality two-dimensional sheets, and for specific materials that require sheets with defined lateral dimensions and thicknesses, such as for use as ink, it is preferable, after peeling, to separate single-layer two-dimensional sheets from thicker layers or those with fewer layers, such as more than 20 layers, or to select the size of the peeled sheets, i.e., to separate smaller sheets from larger sheets.

[0066] According to the present invention, a sheet having the desired size and thickness is selected from the sheet separated from the residual precursor material or from the sheet obtained by peeling off the precursor material and incorporated into the product. Figure 2A and Figure 2B In a continuous production line using equipment.

[0067] Advantageously, flakes can be separated or selected from two-dimensional materials dispersed by centrifugation and sedimentation. In the centrifuged dispersion, the dispersed material is subjected to three forces: centrifugal force, buoyancy, and friction. The thickest and largest flakes have a greater mass and settle more quickly than the smaller and thinner flakes that are therefore lighter. Thus, by adjusting the operating parameters of the centrifuge, flakes with desired lateral dimensions can be maintained in the dispersion.

[0068] In the experimental phase, in order to manufacture exfoliable layered materials having graphene, boron nitride, tungsten disulfide (IV), tungsten diselenide (IV), molybdenum disulfide, bismuth telluride, and other materials, organic dispersion phases such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), alcohols, water with added nonionic and anionic surfactants, and mixtures of alcohols and water, but not limited to these, were used to carry out the methods that are the subject of this invention.

[0069] Reference Figure 3and Figure 4 The following shows the results obtained from the exfoliation of layered materials used to produce nanosheets of two-dimensional materials, particularly the exfoliation of graphite in an NMP dispersion phase.

[0070] The dispersion of graphite in NMP was placed Figure 2A and Figure 2B The supply chamber of the peeling device is shown. The operating parameters of the compression device of the grinding apparatus are set in the range of 10 to 300 MPa, and preferably 200 MPa, and the number of compression paths is programmed between 50 and 250, preferably 250. Of course, different values ​​are possible depending on the concentration of the material in the dispersion, because the amount of peeling material increases with the number of cycles, and also depends on the type of grinding equipment used, especially the diameter of the tube in the grinding apparatus, which is in the range of 0.05 to 1 mm, and preferably between 0.15 and 0.28 mm.

[0071] To separate the still dispersed two-dimensional flakes, the mixture obtained from the grinding process is directly transferred to a separation chamber, in a specific example, an ultracentrifuge, and then, for example, at 20... Centrifuge at 8000 g for 10 minutes at a temperature of C. These process parameters can be modified over a wide range of accelerations, such as from 100 to 1,000,000 g, a wide range of times, such as 5 to 120 minutes, and a wide range of temperatures, such as from 4 to 30°C. C depends on the rheological parameters of the dispersed phase, such as viscosity, and can be between 0.1 and 25 mPa·s.

[0072] While ultracentrifuges are the most suitable device for centrifugal steps in continuous production lines to purify processed materials, other centrifugal techniques such as decanters, trays, solid bowls, or filter tubes and centrifuges can also be used.

[0073] After centrifuging the dispersion, the floating material (supernatant) is extracted from the collection chamber during the separation time to select and characterize thin films with different transverse, surface, and thickness dimensions.

[0074] The obtained dispersions can be characterized using optical absorption and Raman spectroscopy, as well as transmission electron microscopy. Specifically, optical absorption spectroscopy is used to determine the concentration of two-dimensional flakes in the dispersed phase, Raman spectroscopy is used to determine the number of layers and structural quality, i.e., the presence of defects, doping, etc., while electron microscopy is used to determine the lateral and surface dimensions of the flakes thus produced. Of course, other characterization techniques, such as X-ray photoelectron emission, X-ray diffraction, scanning electron microscopy, and atomic intensity microscopy, can also be used to characterize the obtained dispersions.

[0075] Figure 3 This shows a low-resolution image of a graphene sheet obtained from a transmission electron microscope.

[0076] From the examination of the images, the lateral dimensions of the exfoliated nanosheets can be estimated to be between 100 nm and 10 nm. The thickness is between m and has less than 6 layers. By changing the grinding conditions, namely the pressure, the diameter of the tube in the grinding apparatus and the number of cycles, as well as the centrifugation parameters, thin sheets with smaller lateral dimensions can be prepared.

[0077] Figure 4 Raman spectra of graphene flakes deposited on Si / SiO2 at an excitation wavelength of 532 nm, together with the Raman spectrum of graphite, are shown. The inks, including those obtained by the wet blast milling method according to the invention and those obtained using an ultrasonic treatment method according to the prior art, exhibit a combination of two-dimensional flakes having one or more layers.

[0078] As can be seen from the figure, compared with inks obtained through ultrasonic treatment, and specifically with samples obtained through ultrasonic exfoliation where I(D) / I(G) = 1.2, the sample obtained through wet jet milling with I(D) / I(G) = 0.8 exhibits a lower I(D) / I(G) ratio, indicating defects at the edges and basal surfaces. This result demonstrates that graphene inks produced via wet jet milling are of higher quality than those produced through ultrasonic treatment.

[0079] Through experiments, ink with the thus obtained two-dimensional nanosheets was deposited on glass using a drop casting deposition process, and the electrical properties of the graphene sheets produced by wet jet milling were measured. A sheet resistance of approximately 5 Ω / □ was obtained.

[0080] Advantageously, the steps of supplying the layered material and discharging the stripping material can be fully automated, thereby achieving a significant reduction in production time and cost, and the stripping method described above can be carried out in a closed, continuous cycle production line under a controlled atmosphere, providing the possibility of processing two-dimensional materials such as black phosphorus, which is sensitive to air exposure.

[0081] Again, advantageously, the method according to the invention can be used to prepare inks in large quantities, from a few liters to a few cubic meters, with a considerably high productivity (liters / hour). The prospect of producing a large number of two-dimensional materials with different electronic, optical, mechanical, and electrochemical properties opens the way for countless industrial applications, among which printable, wear-resistant, or generally flexible electronic devices, as well as the manufacture of protective layers, coatings, and energy devices, can be mentioned by certainly non-exhaustive examples.

[0082] There is also the possibility of controlling the rheological properties of the dispersion (i.e., viscosity, density, and surface tension), thus enabling the formulation of colloidal suspensions of graphene nanosheets with rheological properties that can be used in printing or coating techniques on rigid or flexible substrates, such as drop casting, dip casting, rod coating, spraying, inkjet printing, flexographic printing, and screen printing, for the manufacture of electronic devices or for energy conversion (e.g., solar cells, fuel cells, thermoelectric cells) or their storage (e.g., batteries, supercapacitors).

[0083] Specifically, the apparatus and method according to the invention make it possible to completely process the precursor material and obtain a yield close to 100%, unlike known stripping methods that involve ultrasonic treatment with very low yields (i.e., at most 10%).

[0084] Of course, without changing the principles of the invention, the embodiments and details of the embodiments may be quite different from those described and illustrated purely by way of non-limiting examples, and therefore will not exceed the scope of protection of the invention as defined by the appended claims.

Claims

1. A system for peeling off layered materials, comprising, in combination: A stripping station (14-22) for operating a dispersion of a volume of layered precursor material includes a wet jet milling apparatus (10). and Downstream of the stripping stations (14-22), a collection station (30, 40) is set up to operate a dispersion of at least partially stripped material of a volume. The stripping stations (14-22) and the collection stations (30, 40) are connected to each other via a fluid communication path (20), and an inserted flow regulating device (50) is present along the fluid communication path (20). The flow regulating device (50) is adapted to adopt a first operating configuration and a second operating configuration, in which the communication path (20) between the stripping station (14-22) and the collection station (30, 40) is interrupted, thereby the stripping station (14-22) is adapted to expose a volume of a dispersion of layered precursor material to a predetermined number of wet jet milling cycles, and the collection station (30, 40) is adapted to extract a certain amount of stripped material from the volume of dispersion that was previously exposed to milling and includes at least partially stripped material; In the second operating configuration, the communication path (20) between the stripping station (14-22) and the collection station (30, 40) is continuous, thereby adapting the stripping station (14-22) to deliver to the collection station (30, 40) a volume of dispersion of material previously exposed to grinding and comprising at least partially stripped material, and arranging the stripping station to be connected to the supply chamber (12) to be supplied with a further volume of dispersion of layered precursor material.

2. The system according to claim 1, wherein, The collection station includes a device (30) for separating the stripped material from the dispersed phase, including sedimentation devices such as centrifuges.

3. The system according to any one of the preceding claims, wherein, The wet jet milling apparatus (10) includes: - A compression device (14) connected to the supply chamber (12) via a feed pipe (16), the compression device (14) being configured to inject a predetermined volume of a dispersion of layered precursor material from the supply chamber (12) into a pipe having a first compression section toward the grinding device (18); and - A grinding device (18) disposed downstream of the compression device (14) and comprising multiple fluid paths adapted to guide the dispersion injected by the compression device (14) into a pipe having a smaller cross-section compared to the first compression section, thereby generating one or more linear jets conveyed toward at least one collision section, wherein the free movement of the layered precursor material in the dispersion and the collision between the jets cause the stripping of the layered precursor material.

4. The system according to claim 3, wherein, The flow regulating device (50) includes a four-way distribution valve adapted to take a first configuration in the supply / discharge phase, wherein the feed pipe (16) from the supply chamber (12) is connected to the compression device (14) of the grinding device (10) and the outlet pipe (20) from the grinding device (18) is connected to the collection station (30, 40); and a second configuration in which the outlet pipe (20) from the grinding device (18) is connected to the compression device (14) in a recirculation configuration and fluid communication toward the collection station (30, 40) is interrupted.

5. The system according to any one of the preceding claims, wherein, The supply chamber (12) is adapted to contain a dispersion of the layered precursor material in a predetermined dispersion phase selected as a function of the layered precursor material.

6. The system according to claim 5, wherein, The dispersed phase has a surface tension close to the surface energy of the layered precursor material that must be peeled off.

7. The system according to claim 5, wherein, The dispersed phase has a Hansen solubility parameter that is close to that of the layered precursor material in Hansen space.

8. The system according to claim 7, wherein, The similarity between the Hansen solubility parameter of the dispersed phase and the Hansen solubility parameter of the layered precursor material is expressed by the following relationship. r 2 = ( D溶剂 - D材料 ) 2 + ( P溶剂 - P材料 ) 2 + + ( H溶剂 - H材料 ) 2 in: p It is the energy from the intermolecular dipole forces between molecules. D It is energy derived from the dispersive forces between molecules. H It is the energy derived from the hydrogen bonds or electron exchange parameters between molecules, and r At 0 and 15 MPa 1 / 2 Between 0 and 10 MPa 1 / 2 More preferably, between 0 and 5 MPa 1 / 2 between.

9. A method for peeling off layered materials, comprising the following steps: - Provides a dispersion of layered precursor materials; and iteratively - In the stripping station (14-22), a volume of the dispersion of the layered precursor material is exposed to a predetermined number of wet jet milling cycles; - Subsequently, the dispersion volume of the material previously exposed to grinding and including at least partial stripping is conveyed to the collection station (30, 40). and A certain amount of stripping material is extracted from the volume of the dispersion conveyed at the collection stations (30, 40). The fluid communication between the stripping station (14-22) and the collection station (30, 40) is alternately adjusted between a first operation phase and a second operation phase. In the first operation phase, the communication is interrupted, during which a volume of a dispersion of layered precursor material is exposed at the stripping station (14-22) to a predetermined number of wet jet milling cycles, and a certain amount of stripped material is extracted at the collection station (30, 40) from a volume of dispersion of material previously exposed to milling and comprising at least partially stripped material. In the second operating phase, the communication is continuous, thereby conveying a volume of dispersion of material previously exposed to grinding and comprising at least partially stripped material from the stripping station (14-22) toward the collection station (30, 40), and a further volume of dispersion of layered precursor material is supplied to the stripping station (14-22).

10. The method of claim 9, further comprising separating the stripped material from the dispersed phase by centrifugal sedimentation.

11. The method according to claim 9 or 10, wherein, The wet jet milling cycle includes injecting a predetermined volume of the layered precursor material dispersion into multiple fluid paths adapted to guide the dispersion and generate one or more linear jets, wherein the free movement of the layered precursor material in the dispersion and the collisions between the jets cause the delamination of the layered precursor material.

12. The method according to any one of claims 9 to 11, wherein, A dispersion of the layered precursor material is obtained in a predetermined dispersed phase having a surface tension close to the surface energy defects of the layered precursor material that must be peeled off.

13. The method according to any one of claims 9 to 11, wherein, A dispersion of the layered precursor material is obtained in a predetermined dispersion phase having a Hansen solubility parameter that is close to the Hansen solubility parameter of the layered precursor material in Hansen space.

14. The method according to claim 13, wherein, The similarity between the Hansen solubility parameter of the dispersed phase and the Hansen solubility parameter of the layered precursor material is expressed by the following relationship. r 2 = ( D溶剂 - D材料 ) 2 + ( P溶剂 - P材料 ) 2 + + ( H溶剂 - H材料 ) 2 in: p It is the energy from the intermolecular dipole forces between molecules. D It is energy derived from the dispersive forces between molecules. H It is the energy derived from the hydrogen bonds or electron exchange parameters between molecules, and r At 0 and 15 MPa 1 / 2 Between 0 and 10 MPa 1 / 2 More preferably, between 0 and 5 MPa 1 / 2 between.

15. The method according to any one of claims 12 to 14, wherein, The precursor material is graphite and the dispersed phase is one of N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), alcohol, water with added nonionic and anionic surfactants, or a mixture of alcohol and water.

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